Inductively coupled plasma ion source with tunable radio requency power

ABSTRACT

In a plasma ion source having an induction coil adjacent to a reactor chamber for inductively coupling power into the plasma from a radio frequency power source and designed for negative and positive ion extraction, a method for operating the source according to the invention comprises providing radio frequency power to the induction coil with a RF amplifier operating with a variable frequency connected to a matching network mainly comprised of fixed value capacitors. In this device, the impedance between the RF power source and the plasma ion source is matched by tuning the RF frequency rather than adjusting the capacitance of the matching network. An option to use a RF power source utilizing lateral diffused metal oxide semiconductor field effect transistor based amplifiers is disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part and claims the benefit ofU.S. patent application Ser. No. 14/028,305, filed Sep. 16, 2013, whichitself claims the benefit of Provisional Patent Application No.61/701,495, filed Sep. 14, 2012, all of whose contents are incorporatedherein for all purposes.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention relates generally to plasma ion sources and moreparticularly to methods for providing RF power, magnetic filtering, andhigh voltage isolation to an inductively coupled plasma ion source

2. Description of the Prior Art

Focused ion beam (FIB) tools are used for nanometer scale precisionmaterial removal. The benefits of FIB tools include nano-scale beamplacement accuracy, a combined imaging and patterning system foraccurate sample registration and pattern placement, and low structuraldamage of the area surrounding the removed volume. However, conventionalFIB systems typically have a maximum removal rate of ˜5 μm³/s thatlimits their usefulness for removing volumes with dimensions exceeding10 μm. Conventional FIB systems are further limited by the low angularintensity of the ion source, so at large beam currents the beam sizedramatically increases from spherical aberration. For high beam currentsand hence high removal rates of material, a high angular intensity isrequired, along with high brightness and low energy spread.

Focused ion beams are often referred to as ‘primary’ ion beams when usedon secondary ion mass spectrometer (SIMS) systems. Here the term‘primary’ is used to differentiate it from the secondary ion beam. Aswith FIB tools, SIMS tools use the focused primary ion beam for precise,sputter removal of atoms and molecules from a material surface. SIMStools are primarily used to determine the spatial distribution ofchemical constituents in the near surface region of a material. Oxygenprimary ion beams are beneficial to enhance the yield of positivelycharged secondary ions from the sample material, and hence enhance thesensitivity of the SIMS measurement. Negatively charged oxygen ionbeams, not only enhance the yield of positively charged secondary ions,but also result in minimal sample charge buildup when the sample is adielectric material. The state-of-the-art SIMS instruments employduoplasmatron ion sources to produce negative oxygen primary ion beams.Duoplasmatrons have insufficient brightness (˜40 Am⁻²sr⁻¹V⁻¹) andlifetime to produce the spatial resolution required for many SIMSapplications. Duoplasmatrons also produce ion beams with a relativelylarge axial energy spread (˜15 eV), which is also problematic whenendeavoring to produce high spatial resolution focused primary ionbeams.

One solution is to use an inductively coupled plasma ion source.Inductively coupled plasma ion sources typically wrap an RF antennaabout a plasma chamber. Energy is transferred by inductively couplingpower from the antenna into the plasma. A RF power supply with 50 Ohmoutput impedance utilizes an impedance matching network so that theoutput of the RF supply can be efficiently coupled to the plasma whichhas an impedance substantially lower than 50 ohms. To extract negativeions from the ion source, it is typically necessary to use a transversemagnetic field near the source aperture to modify the plasma to allownegative ions to leave the plasma and to separate unwanted electronsthat are extracted with the negative ion beam.

Other applications for this type of plasma source include its use as theprimary ion source for Ion Scattering Spectroscopy (ISS), focused andprojection ion beam lithography, proton therapy, and high energyparticle accelerators.

In all cases, a high power density is deposited into the plasma from theantenna in order to create a high density plasma, and the plasma isbiased to a potential of a hundred Volts or higher with respect toground. An ion beam is extracted from a small aperture and isaccelerated through a bias voltage to produce a fine beam of energeticions.

One issue in the design of plasma ion sources is how to create anoptimum magnetic field near the extraction aperture while a high voltagebias is applied to the plasma chamber. A second issue is how to provideradio frequency power to the antenna when the effective impedance of theplasma is very low compared to common RF power supply output impedances.This is especially problematic because the effective impedance of theplasma varies with plasma chamber gas pressure, gas composition, and thechange of state during plasma ignition. A third problem is how tointroduce gas into a reactor chamber that is biased to a high voltagewithout having high voltage breakdown through the input gas line.

Accordingly, the need arises for new designs and methods that provideefficient RF power to plasma ion sources, as well as improve themagnetic filtering and high voltage stability of plasma ion sources.

SUMMARY OF THE INVENTION

The present invention provides a solution for providing RF power toinductively coupled ion sources as well as improved magnetic filteringand high voltage isolation to plasma ion sources biased to high voltage.

In a plasma ion source having an induction coil adjacent to a reactorchamber for inductively coupling power into the plasma from a radiofrequency power source, a method for operating the source according tothe invention comprises providing radio frequency power to the inductioncoil with a RF amplifier operating with a variable frequency connectedto a matching network mainly comprised of fixed value capacitors. Inthis device the impedance between the RF power source and the plasma ionsource is matched by tuning the RF frequency rather than adjusting thecapacitance of the matching network. An option to use a RF power sourceutilizing lateral diffused metal oxide semiconductor field effecttransistor based amplifiers is disclosed.

A magnetic circuit design for coupling magnetic flux into a plasmareactor chamber that is biased to a high voltage is also disclosed. Themagnetic circuit comprises a source of magnetic flux located at groundpotential combined with a high permeability magnetic circuit thatchannels magnetic flux through a high voltage gap to provide magneticflux into a plasma reactor chamber and an exit aperture that is biasedto high voltage. This design has a portion of a magnetic circuit incontact with a plasma reactor chamber that is biased to high voltage,where the circuit can transfer magnetic flux from a second ground basedportioned of a magnetic circuit while electrically isolating the twoportions of the magnetic circuit.

A gas feed insulator design that improves the high voltage standoff byreducing the electric field along the insulator path is furtherdisclosed. This design results in a short path within the insulator inthe direction of the electric field to minimize avalanche breakdownwithin the insulator.

Finally, the patent describes an ion source that allows for negative ionextraction (or positive ions). The negative ion extraction isfacilitated by the transverse magnetic field, that's created by themagnetic circuit. Optimal negative ion generation is achieved with an RFfrequency that's greater than 40 MHz. Impedance matching at 40 MHz orabove, is made significantly easier by using fixed capacitors and avariable RF frequency to achieve the matching. Variable frequencyimpedance tuning also allows the impedance match circuit to be morecompact, lower complexity and power efficient. Variable frequency tuningeliminates the need for mechanically adjustable capacitors that requireservo or stepper motors to drive them, thus minimizing the complexity ofthe impedance matching device.

The foregoing and other objects, features and advantages of theinvention will become more readily apparent from the following detaileddescription of a preferred embodiment of the invention that proceedswith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a side elevation of a plasma ionsource implemented according to teachings of the present invention.

FIG. 2 is a schematic view showing a side elevation of a preferredmagnetic circuit design used in the plasma ion source of FIG. 1.

FIG. 3 is a schematic view showing a side elevation of a preferred gasinlet insulator used in the plasma ion source of FIG. 1.

FIG. 4 is a schematic view illustrating elements of the radio frequencypower source of FIG. 1.

FIG. 5 is a schematic view illustrating elements of the impedancematching network of FIG. 1 according to one embodiment of the invention.

FIG. 6 is a schematic view illustrating elements of the impedancematching network of FIG. 1 according to an alternative embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an inductively coupled plasma source that includes aceramic tube 10, enclosing the plasma chamber 14, welded between a firstupstream metal flange 34 and a second downstream vacuum flange 13.Windings of an RF antenna 16 are wrapped around, but electricallyisolated (e.g. slightly spaced) from, the cylindrical outer walls ofceramic tube 10. As will be further appreciated through the descriptionbelow, RF antenna 16 is further electrically isolated from thecylindrical outer walls of the ceramic tube 10 by filling of the spacebetween them with a dielectric fluid. A split Faraday shield 18surrounds the cylindrical outer walls of ceramic tube 10 and isinterposed between the RF antenna 16 and the ceramic tube 10. Shield 18includes a plurality of slits through the wall of the shield 18 facingthe ceramic tube 10, with a space between the shield 18 and tube 10being filled with the dielectric fluid.

A gas inlet 20 communicates with an upstream opening A in the plasmachamber 14 to supply material that is later formed into a plasma. Plasmachamber 14 is referenced to high voltage while the surrounding RFshielding—e.g. implemented as Faraday shield 18—and RF antenna 16 makingplural windings about the ceramic tube 10, are referenced to ground. Asource of radio frequency power 45, and an impedance matching networkcomprised of multiple capacitors 49 are electrically connected to the RFantenna 16. The impedance matching network 49 uses fixed value highvoltage capacitors in a radio frequency circuit and in some instancestrimmer capacitors may be used to make small adjustment to thecapacitance of portions of this circuit.

The source of radio frequency power 45 can operate over a range offrequencies in the High Frequency and Very High Frequency bands.Preferably, radio frequency power should operate above about 40 Mhz whenpowering a plasma source that contains a magnetic circuit, as this hasbeen found to provide efficiency advantages.

A source electrode of the plasma chamber has an exit aperture B,opposite the side adjacent the gas inlet 20, and is in furthercommunication with an extraction electrode 11 and focusing opticslocated downstream (not shown). Ions extracted from the plasma are thenfocused into a beam and directed downstream within a ceramic vacuumbreak 22. A magnetic circuit consisting of an electromagnetic orpermanent magnet source of a magnetic flux 50, outer magnetic poles 52based at ground potential, and inner magnetic poles 54 biased at thereactor chamber voltage operate to produce a magnetic field near theexit aperture B. This magnetic field can be set to a relatively highstrength to modify the plasma potential to allow for negative ionextraction and separate electrons from the extracted ion beam, or set toa relatively low strength to just limit electron loss to the sourceelectrode and enhance positive ion extraction without significantlymodifying the plasma potential. The plasma tube 10 is attached to thevacuum flange 13 through a non-magnetic tube 56 brazed to the plasmatube 10.

FIG. 2 shows a detailed view of the magnetic circuit. All elements areretained within a can 24 that surrounds the whole assembly and is heldat ground potential. The assembly in this way forms spaces (e.g. spaces26 a, 26 b, 26 c, and 26 d) between the can 24 and the outer surface ofthe plasma chamber 14 and ceramic vacuum break 22 (space 26 a), betweenthe antenna 16 and the Faraday shield 18 (space 26 b), between theceramic plasma tube 10 and the Faraday shield 18 (space 26 c), andparticularly between the outer magnetic poles 54 and the plasma tube 10(space 26 d). All spaces are in fluid communication with one another,and form a fluid circuit, so that a fluid introduced through inlet 28can be pumped through all spaces and exit outlet 30.

Operation of the RF plasma source results in significant power beingdeposited into the plasma and the antenna, which would create thermalissues and failure within the device if efficient heat dissipation werenot implemented. Air cooling may be used, but such is typicallyinefficient within a small space such as that defined by the plasma ionsource. Water cooling is also a possibility for cooling, but it has poordielectric properties and its reactivity with other materials can createproblems. Furthermore, maintaining different parts of the assembly atdifferent voltages also creates operational issues absent adequateinsulation between the parts.

The invention uses a dielectric fluid as a coolant. The dielectric fluidhas been found to exhibit efficient coolant properties when used in theenvironment of the plasma ion source. Furthermore, a dielectric fluidprovides high voltage isolation between the plasma chamber (at highvoltage) and the other parts at ground potential including the outermagnetic poles. The dielectric fluid also can provide high voltageisolation between the antenna and the Faraday shield as well as betweenthe impedance matching network capacitors and the surrounding groundplanes. A cooling circuit is created within the device so that thedielectric fluid circulates between the plasma chamber 14 and the can 24throughout the device, and preferably through spaces 26 a, 26 b, 26 d,and 26 c. Use of the dielectric coolant around the inductively coupledplasma ion source has been found to keep the plasma chamber and antennaoperating at a stable temperature (near room temperature) and reducesthe gaps required for high voltage stability. More specifically, use ofthe dielectric fluid both electrically insulates the plasma chamber, sothat it can be biased to 30 kV and up, and efficiently transfers heataway from the plasma chamber. The advantages of this approach are:

-   -   1. The entire outer surface of the plasma chamber, the impedance        matching network, the magnetic flux source, and the antenna can        have their thermal energy efficiently transferred away from the        ion source.    -   2. The split Faraday shield can be held at ground potential        while maintaining a minimal gap between the shield and the        plasma chamber. Consequently, the antenna can be in close        proximity to the plasma chamber so that power coupling is more        efficient.    -   3. The outer magnetic poles can be held at ground potential        while maintaining a minimal gap between the outer magnetic pole        and the plasma chamber. Consequently, the outer magnetic pole        can be in close proximity to the plasma chamber and the inner        magnetic poles so that magnetic flux is coupled efficiently        between the inner and outer magnetic poles.    -   4. The antenna, and the matchbox and RF amplifier used to drive        the antenna, are ground referenced (i.e. are not biased at the        same potential as the plasma).    -   5. The dielectric fluid is chemically inert and has a very low        power dissipation factor (loss tangent) at RF frequencies. This        is unlike water that is susceptible to large variations in its        loss tangent depending on its purity.

In a preferred embodiment, the dielectric coolant is a fluorinatedfluid, and the pumping flow is between a heat exchanger (or chiller) andthe plasma source. The coolant preferably has a low relativepermittivity (dielectric constant), in the range of between 1 and 3, anda high dielectric strength (e.g. greater than 10 kV/mm). The preferableflow rate through the cooling circuit is between about 0.5 and 1.5gallons per minute, with a most preferred rate of approximately 1gallon/minute.

FIG. 3 is a side elevation view in section of a plasma ion sourceconstructed according to a preferred embodiment of the invention. Likeelements from FIG. 1 are labeled but not discussed further here. Movingdownstream from gas source 20, an insulator conducts gas from the gassource to a leak valve 32 while providing electrical insulation betweenthe gas source and the leak valve. The leave valve 32 supplies a lowpressure (e.g. approximately 10-100 mTorr) gas into the plasma chamber10. The leak valve 32 cuts the pressure of gas in the line from about1-100 psi supplied to the gas inlet 20 and present in the insulator 36to about 10-100 mTorr at the flange 34 and the reactor chamber 14. Aswill be appreciated from a description of FIG. 3, high voltage appliedto downstream flange 13 contributes to the igniting of plasma withinceramic chamber 14. This conducts potential upstream along the plasma sothat ceramic chamber 14, leak valve 32 and flange 34 are electricallycoupled together at the same (high voltage) potential.

An insulator 36 is interposed between the gas source connected to thegas inlet 20 and the downstream plasma source to electrically isolateelements electrically connected to the biased plasma chamber 14 to thegas source at ground potential. The insulator consists of a narrow tubeor capillary that is hermetically sealed to the gas inlet on one end andthe leak valve 32 at the other end. The insulator has a spiral orserpentine path such that the electric field produced between thecomponents biased to high voltage and those at ground potential islargely perpendicular to the path of the tube with a low electric fieldcomponent that is along the path of the tube. The insulator length alongthe spiral or serpentine path is much longer than the voltage droplength so there is a low average electric field along the insulatorpath. The path along the electric field is kept physically short by thenarrow tube diameter so avalanche breakdown is suppressed. The gaspressure within the insulator is between about 1-100 psi and the highpressure in combination with the short avalanche breakdown path in theinsulator prevents the gas from breaking down when holding off the biasvoltage. Accordingly, everything on top of the insulator 36 in FIG. 3 ismaintained at ground while that below the insulator is kept at the highvoltage applied.

In one aspect of the invention, the plasma tube 10 is electricallyisolated from ground by a combination of mechanical insulating supportstructures and the dielectric fluid. The insulating support structuresare configured to position the plasma tube 10 containing the innermagnetic poles 54 within the assembly so that it does not touch can 24,shield 18, RF antenna 16, outer magnetic poles 52, or other elementsheld at a different potential. Examples of such insulated supportstructures include ceramic vacuum break 22 and insulator 36 (FIG. 2). Anexternal high voltage (between 0 and 50 kV) is applied to the plasmatube and the current design uses the dielectric fluid to isolate theplasma tube at applied voltage from the Faraday shield 18, antenna 16,and other structures in the source at ground potential. This design isunique in that each of the plasma tube, the antenna, and the impedancematching network is electrically isolated and cooled by the dielectricfluid.

Another aspect of the design is that the plasma tube is substantially orcompletely immersed into the dielectric fluid so that the fluid caneffectively transfer heat away from the plasma tube, antenna, andimpedance matching network. In wafer processing configurations, thewhole plasma chamber may not be immersed in fluid but typically anantenna is immersed in fluid and a dielectric window near the antenna ispartially immersed in fluid. However, most of the chamber containing theplasma is not immersed in fluid.

In the present design, ions are removed from the plasma and then theions interact with a substrate outside of the plasma. The externalvoltage is applied to control how energetic the ions are when theyinteract with the substrate. The ions are typically focused anddeflected after they have been extracted from the plasma. The presentdesign includes a means for extracting the ions and accelerating theions to the applied voltage.

Also described is a method for operating a plasma ion source havinginduction coils adjacent to outer walls of a reactor chamber forinductively coupling power into the plasma from a radio frequency powersource. The method comprises actively biasing the reactor chamber to ahigh voltage and pumping a dielectric fluid into contact with theinduction coils and a substantial portion of the outer walls of thereactor chamber wherein both the reactor chamber and induction coils areelectrically isolated and cooled by the dielectric fluid. The step ofactively biasing the reactor chamber to a high voltage preferablyincludes biasing the reactor chamber to a voltage above 10 kV.

The dielectric fluid can be pumped in a circuit through a plurality ofspaces in fluid communication with one another. The plurality of spacesinclude a space adjacent the induction coils, a space adjacent outerwalls of the reactor chamber, and a space adjacent a vacuum breakdownstream of the reaction chamber. The method further preferablyincludes enclosing the induction coils with a split Faraday shield andenclosing the Faraday shield, reaction chamber, and vacuum break in acan to retain the dielectric fluid. The Faraday shield is preferablymaintained at a ground potential. The circuit through which dielectricfluid is pumped includes a space between the can and the vacuum breakand the can and plasma chamber.

The method can further include maintaining different elements of theplasma ion source at different voltages and providing a high voltageisolation between the antenna and Faraday shield. Furthermore, the stepof pumping the dielectric fluid includes pumping the fluid through acircuit into and out of the plasma ion source at a rate of between about0.5 and 1.5 gallons per minute and more preferably approximately 1gallon/minute.

FIG. 4 illustrates an exemplary source of radio frequency power 45 asused in association with the plasma ion source shown in FIG. 1.

Generation of the RF oscillation within the RF power source 45 beginswith the variable frequency oscillator block 60, which in one embodimentis implemented using a reference crystal oscillator and direct digitalsynthesizer (DDS) integrated circuit. Other implementations couldsubstitute a voltage controlled oscillator (VCO) and/or a phase lockloop (PLL) integrated circuit. Any of these take a digital frequencycontrol number (direct command or a number to a D to A convertor) fromthe microcontroller 62. The user controls the frequency setting throughthe external interfaces 64 or through a frequency control (knob,buttons, touch panel interface, etc.) as via controls and display 66.Alternately, the frequency setting of block 60 is set by themicrocontroller software, which is programmed to determine the frequencyto use.

From the oscillator 60, the RF power level is adjusted by the variableattenuator 68 and raised to the output power level by succeedingamplifier stages 70 as needed. The final amplifying stage preferablyuses two N channel lateral drain metal oxide semiconductor field effecttransistors (LDMOSFETs) in a single package to raise the RF power to itshighest level. This provides high power gain and high output with asimple, small, and rugged amplifier stage. Higher frequency harmonics ofthe operating frequency are optionally reduced by a low pass filter 72and the output signal is sent through the directional coupler 74 on theway to the output connection 76. Thereafter the signal is conducted tothe matching network 49 (FIG. 1) either through a coax cable 90 (FIG.5), or in the case of the RF generator being located on the side of theplasma source column 24 (FIG. 1), the RF power may be connected with twoshort individual connections (signal and return). The forward powersignal from the directional coupler 74 passes through RF detector 78 andprovides feedback to the RF power control circuit 80 though line 2,which adjusts the variable attenuator 68 in order to maintain the powerlevel commanded by the microcontroller 62.

The reflected power signal from the directional coupler 74 passedthrough RF detector provides feedback to the user—e.g. on a display 66or remotely through the external interfaces 64—as to how well matchedthe system is at the present operating frequency. Optionally, anautomatic tuning algorithm running on the microcontroller 62 does thesame. Using this number, the user or algorithm can adjust the frequencyto the optimum, minimum reflected power point.

The circuit is completed by coupling microcontroller 62 and RF amplifierstages 70 to power source 82.

FIG. 5 illustrates a first embodiment of an impedance matching network49 used in association with the plasma ion source shown in FIG. 1. Thisimpedance matching network 49 is incorporated into a lateral projectionof a generally cylindrical source enclosure or can 24 (FIG. 1) intowhich the antenna coil 16 is placed. The load and tune capacitors of theimpedance matching network 49 each include a main fixed capacitor 86 f,88 f, respectively, coupled in parallel with a respective trim capacitor86 t, 88 t. In the case that the capacitance of the “fixed” capacitors86 f, 88 f are not exactly fixed on the value advertised, e.g. that alabelled “100 μf capacitor” is actually 99.6 μf, the supplemental trimcapacitors can be incorporated to bring the circuit up to the specified100 μf. In this way, the network 49 can impart capacitance with highprecision since the trim capacitors 86 t, 88 t can be adjusted to bringthe fixed capacitors 86 f, 88 f to their needed values. Impedancematching network 49 is then coupled to the variable frequency RFgenerator 45 via a coax cable connection 90. A dielectric fluid is thenflowed through a circuit in adjacent to or in contact with the plasmasource 24 and the impedance matching network 84 to effect cooling of theapparatus during high energy operation.

FIG. 6 illustrates a second embodiment of an impedance matching network49 used in association with the plasma ion source shown in FIG. 1. Thisembodiment is much like that shown in FIG. 5, but has much of the RFpower source 45 located against the source enclosure and sharing contactwith the cooling fluid.

The ‘output’ shown in FIG. 6 is the same connection as is satisfied bythe coax cable and the RF connector 90 in FIG. 5, and the ‘ground’connection in FIG. 6 is the same as item 24 in FIG. 1. In the embodimentshown in FIG. 1, the RF signal is fed into the matchbox (49) via thecentral wire of the coax cable. The outer shield of the coax cable(which is connected to item 24) carries the return current to the RFgenerator. Item 24 is at ground potential and is connected to the outershield of the coax cable.

In the embodiment shown in FIG. 6, there's no need for a coax cable orthe coax cable connector (90), and instead the RF generator is directlyattached to the match circuit, where the ‘output’ connects directly tothe same point in the match circuit that the RF signal is connected toin FIG. 1. For FIG. 6, the return current still travels through item 24,back to the ground connection of the RF generator, but it no longerneeds to travel through the outer shield of a coax cable.

Having described and illustrated the principles of the invention in apreferred embodiment thereof, it should be apparent that the inventioncan be modified in arrangement and detail without departing from suchprinciples. We claim all modifications and variation coming within thespirit and scope of the following claims.

1. A plasma source for processing or imaging a substrate, secondary ionmass spectrometry, ion source for proton therapy, and high energyparticle accelerators comprising: a reactor chamber within which aplasma is generated to produce at least one plasma product forprocessing or imaging the substrate, secondary ion mass spectrometry,ion source for proton therapy, ion thrusters, and high energy particleaccelerators, the reactor chamber including outer walls that areactively biased to a high voltage; a gas source coupled to the reactorchamber to provide gas into the reaction chamber; an exit aperturecoupled to the reactor chamber to allow extraction of ions from thereactor chamber; a first source of radio frequency power with tunableradio frequency; a plurality of induction coils adjacent to the reactorchamber and coupled to said first source of radio frequency power toinductively couple power into the plasma from said first source of radiofrequency power through an impedance matching network comprised of fixedcapacitors that are not variable, wherein the frequency of the power isadjusted to allow efficient power coupling between the source of radiofrequency power and the plasma source.
 2. The plasma source of claim 1,further including one or more trim capacitors in the impedance matchingnetwork.
 3. The plasma source of claim 2, the one or more trimcapacitors arranged in parallel with a respective one of the fixedcapacitors.
 4. The plasma source of claim 1, wherein the impedancematching network is in contact with a dielectric fluid to thermally cooland electrically isolate the impedance matching network.
 5. The plasmasource of claim 1, wherein the source of radio frequency power is incontact with a dielectric fluid to thermally cool and electricallyisolate the source of radio frequency power.
 6. The plasma source ofclaim 5, wherein laterally diffused metal oxide semiconductor fieldeffect transistors are used to produce power in the radio frequencypower source.
 7. The plasma source of claim 1, wherein lateral drainmetal oxide semiconductor field effect transistors (LDMOSFETs) are usedto produce power in the radio frequency power source.
 8. The plasmasource of claim 7, wherein a final stage of the first source of radiofrequency power includes two or more LDMOSFETs in a single package toraise the RF power to its highest level.
 9. The plasma source of claim1, wherein the power source includes a variable frequency oscillatorblock uses a reference crystal oscillator and direct digital synthesizer(DDS) integrated circuit.
 10. The plasma source of claim 1, wherein thepower source includes a variable frequency oscillator block uses avoltage controlled oscillator (VCO).
 11. The plasma source of claim 10,wherein the power source includes a variable frequency oscillator blockuses a phase lock loop (PLL) integrated circuit.
 12. The plasma sourceof claim 1, wherein the power source includes a variable frequencyoscillator block uses a phase lock loop (PLL) integrated circuit.